I understand your perspective and don't take these concerns lightly - I was a refugee of two wars myself, so I'm deeply aware of human suffering and its impact. Our mission to humanize the web means ensuring universal access to human knowledge, regardless of politics, delivered with clarity and protected with integrity - for everyone, regardless of their location or circumstances. A search engine that filters sources by political approval becomes something else entirely - it becomes a biased information provider that denies the very universal access we're fighting for. The most humane thing we can do is build tools that serve humans first by providing the best possible search results to everyone - before this conflict, after this conflict, and during all other 100+ armed conflicts taking place in the world today.
The thing to keep in mind is that for some people, and this includes some of your customers, there are things that are more important than your mission. Right now, some people avoid anything that is related to Israel. When the US invaded Iraq, some avoided US companies. I won't touch anything related to Musk after the two sieg heils and other things. The guy that complained clearly has an issue with what Russia is doing in Ukraine and doesn't want their money to end up in Russia.
It's a free market. You should do what you think it's right and then people will do the same with your product. Some will care more about search quality and pay, while others will care about the companies you decide to work with and use something else.
Would it be possible for users to opt out of Yandex, thus removing any Yandex results from their searches? We can do this with specific websites, why not yandex?
An upstream search index is not exactly a source and boy is that one politically biased. Given Russia's efforts towards destruction of civic society everywhere and replacing it with post-truth one, you very much risk compromising integrity by touching their products.